Lesson 7.03 Soils Around the World

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Looking at primary succession will help you understand how soil formation occurs and how climate and native species influence soil type. Primary succession is soil formation that begins on bare rock.

Think back to the time-lapse video in the previous lesson and how humus formed on a sand and gravel base. A pioneer species, such as lichen, starts to grow on the rock and breaks it down by chemical weathering. This allows physical weathering, such as frost action and abrasion, to take effect on the rock. These processes begin forming the base parent material - inorganic material - for the eventual soil. The type of parent material will give the soil some of its properties such as color and texture. When the lichens die, they contribute organic matter - humus - to the soil mix and a soil layer begins to develop.

As the soil layers begin to develop and increase, small plants, such as mosses, grasses, and small shrubs are able to grow in the soil. The type of small plants depend on the climate. The roots from these plants continue the process of breaking down the bedrock, turning it into more parent material for the soil. The plants also contribute organic material to the soil when they die or shed leaves.

The types of plants that exist in an area also contribute to soil characteristics, such as color, nutrient levels, and pH. An example of plant material determining soil characteristics can be seen in the taiga biome. Trees in the taiga have needle-like leaves that drop to the ground. These leaves are acidic which decreases the pH of the soil making it more acidic. Remember that acidity also affects the types of plants that can grow in these areas. Plant types influence the type of animal life that will exist in the area, and animals can also influence soil makeup and characteristics.

A biome will eventually reach its climax community, which is a mature community where the type/species of plant life and animal life remain stable. Climax communities result in the different biomes - tropical rainforest, grassland, deciduous forest, desert, tundra, and taiga. Which climax community a certain area will be depends on the climate. The type of climax community is influenced by the climate and the type of soil but also contributes to the soil characteristics for that area. The soil characteristics remain stable when the climax community is reached.

View Quia: Primary and Secondary Succession to see examples of primary succession. Be sure to scroll through all of the examples.

Soil types differ from region to region based on the type of parent material and the climate of the area. Soil profiles differ based on these same factors. Notice how the soil profiles differ between these 4 different climates. Notice how the topsoil horizons differ in size and color between these different climates: the prairie soil profile shows a much deeper and darker layer of topsoil than the others. The soil of grasslands is "richer"/higher in nutrients than the other soils because of the climate and type of plants growing in the soil. This shows that climate and plant life play an important role in determining the makeup/composition of soil.

Image citation:
Soil profiles in different climates University of Georgia Geology Department. Web. 29 June 2015. <http://www.gly.uga.edu/>.

Within the state of Alabama itself, soil types and composition differ. This is largely based on the type of parent material from which each soil type is derived.

Open the USDA Natural Resource Conservation Service's report on the Soils of Alabama and read about the seven major soil areas in Alabama. The article includes information about each area's parent material and the type of crops that generally grow in each area. The second page contains a map of the different soil areas.

Soils are classified based on characteristics, such as color, texture, and mineral composition. The current method of classifying and naming soils based on their physical and chemical characteristics is called the soil taxonomy system.

Complete 7.03 Soils around the World Notes while you read through all of the information below. This notes chart with help you with the tasks for this lesson as well as serve as a study guide for the test.

Visit The Twelve Soil Orders to read about the beginning and evolution of the current soil taxonomy system. After reading about the system, click on Information about each of the 12 soil orders and read about the different soil orders and where they are found. You can also see maps of where each order and suborder of soil is located within the United States. Pay attention to the type percentage of soil that each order makes up in the United States.

Next, visit the USDA's The Twelve Orders of Soil Taxonomy and click on each picture to read more about the characteristics of each soil order. Pay attention to each soil's basic characteristics, type of ideal climate, and global percentage.

Finally, visit PBS's Soils Around the World interactive. Launch the interactive, read Introduction to Soils, and then click Begin. Interact with the map and images to read about each soil order. (Helpful hint: after selecting the color for each one, unselect it by clicking on it again so that the map will not become too crowded and you can better see whee each soil type is located.)